Sionna Therapeutics, Inc.

Previous wording

In June 2025, we announced positive topline data from our two randomized, double-blinded, placebo-controlled Phase 1 clinical trials evaluating SION-719 and SION-451, our lead NBD1 stabilizer product candidates, in healthy volunteers, and our plans to advance both compounds to the next phase of clinical development. The trials assessed the safety, tolerability, and pharmacokinetics ("PK") of single and multiple ascending doses of each product candidate, as well as food effect and tablet bioequivalence.

Current wording

In June 2025, we announced positive topline data from our two randomized, double-blind, placebo-controlled Phase 1 clinical trials evaluating SION-719 and SION-451, our lead NBD1 stabilizer product candidates, in healthy volunteers, and our plans to advance both compounds to the next phase of clinical development. The trials assessed the safety, tolerability, and pharmacokinetics ("PK") of single and multiple ascending doses of each product candidate, as well as food effect and tablet bioequivalence.

Previous wording

Due to our significant research, development and manufacturing expenditures, we have accumulated substantial losses and negative cash flows since our inception, including net losses of $26.8 million and $16.5 million for the three months ended March 31, 2026, and 2025, respectively. As of March 31, 2026, we had an accumulated deficit of $283.1 million.

Current wording

Due to our significant research, development and manufacturing expenditures, we have accumulated substantial losses and negative cash flows since our inception, including net losses of $56.7 million and $34.6 million for the six months ended June 30, 2026, and 2025, respectively. As of June 30, 2026, we had an accumulated deficit of $313.0 million.

Previous wording

As of March 31, 2026, we had cash, cash equivalents and marketable securities of $289.9 million. Based upon our current operating plans, we believe that our existing cash, cash equivalents and marketable securities will be sufficient to fund our operations into 2028. We have based this estimate on assumptions that may prove to be wrong, and we could exhaust our available capital resources sooner than we expect. In addition, we could utilize our available capital resources sooner than we expect. See the sections titled “—Liquidity and Capital Resources” and “Risk Factors—Risks Related to Our Limited Operating History, Financial Condition and Need for Additional Capital” included elsewhere in this Quarterly Report.

Current wording

As of June 30, 2026, we had cash, cash equivalents and marketable securities of $268.3 million. Based upon our current operating plans, we believe that our existing cash, cash equivalents and marketable securities will be sufficient to fund our operations into 2028. We have based this estimate on assumptions that may prove to be wrong, and we could exhaust our available capital resources sooner than we expect. See the sections titled “—Liquidity and Capital Resources” and “Risk Factors—Risks Related to Our Limited Operating History, Financial Condition and Need for Additional Capital” included elsewhere in this Quarterly Report.

Previous wording

•external expenses, including expenses incurred under arrangements with third parties, such as contract research organizations, contract development and manufacturing organizations, consultants and our scientific advisors;

Current wording

•external expenses, including expenses incurred under arrangements with third parties, such as contract research organizations, contract development and manufacturing organizations, consultants and our scientific and clinical advisors;

Previous wording

We recognize research and development costs in the periods in which they are incurred. Most of our research and development expenses have been related to identifying and developing our product candidates. Typically, external expenses are recognized based on an evaluation of the progress to completion of specific tasks using information provided to us by our service providers as of each reporting date. Advance payments that we make for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses, which are expensed as the related goods are delivered or the services are performed, or when it is no longer expected that the goods will be delivered, or the services rendered. Significant judgments and estimates are made in determining the accrued, or prepaid expense balances at the end of any reporting period.

Current wording

We recognize research and development costs in the periods during which they are incurred. Most of our research and development expenses have been related to identifying and developing our product candidates. Typically, external expenses are recognized based on an evaluation of the progress to completion of specific tasks using information provided to us by our service providers as of each reporting date. Advance payments that we make for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses, which are expensed as the related goods are delivered or the services are performed, or when it is no longer expected that the goods will be delivered or the services rendered. Significant judgments and estimates are made in determining the accrued or prepaid expense balances at the end of any reporting period.

Previous wording

External costs represent a significant portion of our research and development expenses, which we track on a program-by-program basis following the nomination of a product candidate. Our internal research and development expenses consist primarily of personnel-related expenses, including stock-based compensation expenses and allocated expenses. We do not track our internal research and development expenses on a program-by-program basis as they either relate to early-stage research expenses, such as lab supplies or our personnel expenses, consulting fees or other costs that are deployed across multiple programs.

Current wording

External costs represent a significant portion of our research and development expenses, which we track on a program-by-program basis following the nomination of a product candidate. Our internal research and development expenses consist primarily of personnel-related expenses, including stock-based compensation expenses and allocated expenses. We do not track our internal research and development expenses on a program-by-program basis because they either relate to early-stage research expenses, such as lab supplies or our personnel expenses, consulting fees or other costs that are deployed across multiple programs.

Previous wording

•direct research and development expenses increased by $2.5 million primarily due to an increase in clinical programs and combination development activities; and

Current wording

•direct research and development expenses increased by $4.0 million primarily due to an increase in clinical programs and combination development activities; and

Previous wording

•unallocated research and development expenses increased by $2.7 million primarily due to a $2.3 million increase in personnel-related expenses including stock-based compensation, driven by an increase in the size of our workforce to support our clinical pipeline.

Current wording

•unallocated research and development expenses increased by $2.5 million primarily due to a $2.2 million increase in personnel-related expenses including stock-based compensation, driven by an increase in the size of our workforce to support our clinical pipeline.

Previous wording

General and administrative expenses increased by $4.6 million to $10.6 million for the three months ended March 31, 2026, from $6.0 million for the three months ended March 31, 2025. The increase in general and administrative expenses was primarily due to:

Current wording

General and administrative expenses increased by $4.1 million to $10.6 million for the three months ended June 30, 2026, from $6.5 million for the three months ended June 30, 2025. The increase in general and administrative expenses was primarily due to:

Previous wording

Interest income decreased by $0.2 million to $2.8 million for the three months ended March 31, 2026, from $3.0 million for the three months ended March 31, 2025, primarily due to lower average balances of cash, cash equivalents and investments in marketable securities, reflecting the use of such balances to fund operating expenses.

Current wording

Interest income decreased by $1.1 million to $2.6 million for the three months ended June 30, 2026, from $3.7 million for the three months ended June 30, 2025, primarily due to lower average balances of cash, cash equivalents and investments in marketable securities, reflecting the use of such balances to fund operating expenses.

Previous wording

As of March 31, 2026, we had $289.9 million in cash, cash equivalents and marketable securities.

Current wording

As of June 30, 2026, we had $268.3 million in cash, cash equivalents and marketable securities.

Previous wording

For the three months ended March 31, 2026, net cash used in operating activities was $21.8 million primarily due to our net loss of $26.8 million and changes in operating assets and liabilities of $2.1 million, partially offset by $7.0 million of net non-cash charges, which includes stock-based compensation, depreciation, non-cash operating lease expense and amortization of discounts on marketable securities.

Current wording

For the six months ended June 30, 2026, net cash used in operating activities was $44.1 million primarily due to our net loss of $56.7 million and changes in operating assets and liabilities of $1.7 million, partially offset by $14.3 million of net non-cash charges, which includes stock-based compensation, depreciation, non-cash operating lease expense and amortization of discounts on marketable securities.

Previous wording

For the three months ended March 31, 2025, net cash used in operating activities was $16.3 million primarily due to our net loss of $16.5 million and changes in operating assets and liabilities of $1.9 million, partially offset by $2.0 million of net non-cash charges, which includes stock-based compensation, depreciation, non-cash operating lease expense and amortization of discounts on marketable securities.

Current wording

For the six months ended June 30, 2025, net cash used in operating activities was $34.4 million primarily due to our net loss of $34.6 million and changes in operating assets and liabilities of $4.2 million, partially offset by $4.4 million of net non-cash charges, which includes stock-based compensation, depreciation, non-cash operating lease expense and amortization of discounts on marketable securities.

Previous wording

Net cash provided by investing activities was $24.8 million during the three months ended March 31, 2026, which was primarily driven by maturities of marketable securities of $50.1 million, partially offset by purchases of marketable securities of $25.3 million.

Current wording

Net cash provided by investing activities was $46.3 million during the six months ended June 30, 2026, which was primarily driven by maturities of marketable securities of $104.6 million, partially offset by purchases of marketable securities of $58.4 million.

Previous wording

Net cash used in investing activities was $141.2 million during the three months ended March 31, 2025, which was primarily driven by purchases of marketable securities of $171.6 million, partially offset by maturities of marketable securities of $30.5 million.

Current wording

Net cash used in investing activities was $164.4 million during the six months ended June 30, 2025, which was primarily driven by purchases of marketable securities of $228.0 million, partially offset by maturities of marketable securities of $63.7 million.

Previous wording

Net cash provided by financing activities was $1.9 million during the three months ended March 31, 2026, primarily due to exercise proceeds totaling $2.2 million, partially offset by payments of deferred offering costs of $0.3 million related to the sales agreement entered into in March 2026.

Current wording

Net cash provided by financing activities was $2.6 million during the six months ended June 30, 2026, primarily due to exercise proceeds totaling $3.2 million, partially offset by payments of deferred offering costs of $0.6 million related to the sales agreement entered into in March 2026.

Previous wording

Net cash provided by financing activities was $202.4 million during the three months ended March 31, 2025, during which time the Company closed its initial public offering.

Current wording

Net cash provided by financing activities was $202.1 million during the six months ended June 30, 2025, during which time the Company closed its initial public offering.

Previous wording

As of March 31, 2026, we had cash, cash equivalents and marketable securities of $289.9 million. Based upon our current operating plans, we believe that our existing cash, cash equivalents and investments in marketable securities, will be sufficient to fund our operations into 2028. However, our forecast for the period of time through which our financial resources will be adequate to support our operations is a forward-looking statement that involves risks and uncertainties, and actual results could vary materially. Additionally, conducting preclinical studies and clinical trials is costly, and the timing of progress and expenses in these studies and trials is uncertain. We will need to raise substantial additional capital in the future.

Current wording

As of June 30, 2026, we had cash, cash equivalents and marketable securities of $268.3 million. Based upon our current operating plans, we believe that our existing cash, cash equivalents and investments in marketable securities, will be sufficient to fund our operations into 2028. However, our forecast for the period of time through which our financial resources will be adequate to support our operations is a forward-looking statement that involves risks and uncertainties, and actual results could vary materially. Additionally, conducting preclinical studies and clinical trials is costly, and the timing of progress and expenses in these studies and trials is uncertain. We will need to raise substantial additional capital in the future.

Previous wording

•the timing and amount of milestones, royalties, or other payments we may be required to make to third parties, including Sanofi SA, the Cystic Fibrosis Foundation and AbbVie, and the terms and timing of establishing and maintaining any other similar arrangements we may enter in the future;

Current wording

•the timing and amount of milestones, royalties, or other payments we may be required to make to third parties, including Sanofi SA, the Cystic Fibrosis Foundation and AbbVie, and the terms and timing of establishing and maintaining any other similar arrangements we may enter into in the future;

Previous wording

During the three months ended March 31, 2026, we evaluated certain contractual arrangements with a contract manufacturing organization and recognized related costs during the period. We evaluate such arrangements on an ongoing basis. Other than this matter, there were no material changes to our contractual obligations and commitments described under "Management’s Discussion and Analysis of Financial Condition and Results of Operations" in the Annual Report.

Current wording

During the six months ended June 30, 2026, we evaluated certain contractual arrangements with a contract manufacturing organization and recognized related costs during the period. We evaluate such arrangements on an ongoing basis. Other than this matter, there were no material changes to our contractual obligations and commitments described under "Management’s Discussion and Analysis of Financial Condition and Results of Operations" in the Annual Report.

Previous wording

During the three months ended March 31, 2026, there were no material changes to our critical accounting estimates described under "Management’s Discussion and Analysis of Financial Condition and Results of Operations" in the Annual Report.

Current wording

During the six months ended June 30, 2026, there were no material changes to our critical accounting estimates described under "Management’s Discussion and Analysis of Financial Condition and Results of Operations" in the Annual Report.

Previous wording

We are also a “smaller reporting company” as defined in the Exchange Act. We may continue to be a smaller reporting company even after we are no longer an emerging growth company. We may take advantage of certain of the scaled disclosures available to smaller reporting companies until for so long as either (i) our voting and non-voting common stock held by non-affiliates is less than $250.0 million measured on the last business day of our second fiscal quarter, or (ii) our annual revenue is less than $100.0 million during the most recently completed fiscal year and our voting and non-voting common stock held by non-affiliates is less than $700.0 million measured on the last business day of our second fiscal quarter.

Current wording

We are also a “smaller reporting company” as defined in the Exchange Act. We may take advantage of certain of the scaled disclosures available to smaller reporting companies for so long as either (i) our voting and non-voting common stock held by non-affiliates is less than $250.0 million measured on the last business day of our second fiscal quarter, or (ii) our annual revenue is less than $100.0 million during the most recently completed fiscal year and our voting and non-voting common stock held by non-affiliates is less than $700.0 million measured on the last business day of our second fiscal quarter. Based on the market value of our common stock held by our non-affiliates as of June 30, 2026, we will no longer be a “smaller reporting company” as of January 1, 2027, but remain eligible to use the requirements of a smaller reporting company until our Quarterly Report on Form 10-Q for the quarter ending March 31, 2027.